Colorado River Basin Water Supply & Demand Study
Technical Updates

These reports were initially published in June 2011 under Interim Report No. 1 and have since been updated to reflect the comments received on Interim Report No. 1, technical developments, and the ongoing input of stakeholders.

This report describes the water supply scenarios and presents the analysis and comparison of those scenarios.

Substantive changes made to this report since its first publication as part of Interim Report No. 1 are noted below by section.

Historical Supply (Section 4) – Information related to watershed elevation was added and discussion related to the Pacific Decadal Oscillation and El Nino-Southern Oscillation relationships to streamflow in the Colorado River was expanded. Recent updates to the observed natural flow record for the Colorado River at Lees Ferry resulted in a reclassification of the recent drought.

Future Supply under Downscaled GCM Projected Scenario (Section 8) – Evaluated biases in GCM-projected precipitation and temperature and streamflow simulated by the Variable Infiltration Capacity (VIC) hydrology model. Applied a correction to account for the biases in the VIC-simulated streamflows. Additionally, the method to generate daily precipitation and temperature for input to the VIC model was modified. A more in-depth analysis was conducted to better understand 1) the relative sensitivity of results to emission scenarios driving the GCM output, and 2) extreme high annual flows projected under this scenario.

Supplemental Analysis of Future Climate Data (Appendix B3) – New appendix that describes supplemental analysis of biases in GCM-projected precipitation and temperature, and its potential influence on streamflow.

This report describes the metrics that have been identified for use in the assessment of the reliability of the system to meet the needs of the resources under future demand and supply scenarios.

Substantive changes made to this report since its first publication as part of Interim Report No. 1 are noted below by section.

Water Deliveries Metrics (Section 4) – Metrics have been added including those that measure the ability of the system to satisfy tribal water rights.

Water Quality Resources Metrics (Section 6) – Metrics have been added to include the measurement of salinity in the Upper Basin and one additional location in the Lower Basin.

Recreational Resources Metrics (Section 8) – Metrics have been developed and added that provide the ability of a quantitative assessment of river and whitewater boating.

Ecological Resources Metrics (Section 9) – Metrics have been developed and added for all attributes of interest. In particular, two new groups of metrics were added to the aquatic and riparian habitat attribute of interest, cottonwood recruitment and flow-dependent ecological systems. In addition, metrics described in Interim Report No. 1 were further refined.